Process for the catalytic cleavage of vegetable oils

ABSTRACT

Process for the production of saturated monocarboxylic acids and triglycerides of saturated carboxylic acids having more than one acid function starting from non-modified vegetable oils containing triglycerides of unsaturated fatty acids, comprising the oxidative cleavage of the unsaturated fatty acids.

The present invention relates to a process for the production ofsaturated monocarboxylic acids and triglycerides of saturated carboxylicacids having more than one acid function starting from non-modifiedvegetable oils containing triglycerides of unsaturated fatty acids,comprising the oxidative cleavage of the unsaturated fatty acids.

Oxidative cleavage processes starting from unsaturated fatty acids ortheir derivatives such as, for example, esters of unsaturated fattyacids are known in the literature. They typically comprise a first step(a) in which the olefinic double bond of the unsaturated fatty acid isoxidised to form a vicinal diol, and a second step (b) in which the bondbetween the two carbon atoms of the vicinal diol moiety is cleaved.

A process of this type is described in EP 0 666 838. In such process theoxidative cleavage is characterised in that both the steps (a) and (b)are performed without any added organic solvent, and in that during step(b) water is added to the reaction product of step (a), thus obtaining amixture with a water/diol ratio of between 1:1 and 5:1, then reactingthe mixture with oxygen, or a compound containing oxygen, in thepresence of a cobalt compound as catalyst. This process does not requireany purification of the intermediate reaction product (vicinal diol) anddoes not require the addition of solvents for oxidation of the diol,which is performed in the presence of water. The characteristics of theintermediate product that forms at the end of the first step, inparticular its high viscosity, nevertheless make it necessary to addlarge quantities of water in order to perform the second step of theprocess. From the point of view of industrial production, this fact isparticularly disadvantageous as it involves the need for large-volumereactors. Moreover, the high amount of residual water and the presenceof organic residues at the end of the process require a burdensometreatment to recover the dissolved catalyst and dispose of it due to.

A different process for the preparation of saturated carboxylic acids byoxidative cleavage is described in the patent application WO 2007/039481A1.

According to said application, the oxidative cleavage process ischaracterised by the use, as starting material, of a derivative—inparticular a methyl ester—of a monounsaturated fatty acid. The use ofsaid derivative as starting material produces a less viscous reactionintermediate than the process according to EP 0 666 838, thus making itpossible to reduce the amount of water required. The use of saidderivative as starting material requires, however, that a reaction oftransesterification of the triglycerides contained in the startingvegetable oil is performed upstream the process. The need for saidtransesterification reaction upstream the oxidative cleavage process hasobvious disadvantages of an economic nature. On the one hand the need touse toxic solvents such as methyl alcohol requires appropriate safetymeasures which significantly affect costs. On the other, the productionof glycerol as a by-product of the reaction implies the need to identifyoutlet markets for the latter. Furthermore, the components present atthe end of this process require, for their separation, the use oftechniques that exploit their different solubility in water and, fortheir purification, the use of distillation processes such as, forexample, fractional distillation.

A process for the preparation of saturated aliphatic carboxylic acids byoxidative cleavage of unsaturated aliphatic carboxylic acids isdescribed in EP 0 128 484 A1. Said process comprises subjectingunsaturated aliphatic monocarboxylic acid, fatty acid mixtures producedby hydrolyzing vegetable oils, tall oil fatty acids and esters of thesefatty acids to a first reaction with peroxides and to a followingoxidation by oxygen in the presence of a catalyst comprising at leastone heavy metal compound and at least one member selected from the groupof a bromine compound and a chlorine compound.

Therefore, the need is felt for a process that avoids the disadvantagesof the known processes described above.

With the process according to the present invention, it has beensurprisingly discovered that it is possible to produce saturatedmonocarboxylic acids and triglycerides of saturated carboxylic acidshaving more than one acid function starting directly from vegetable oilswithout the need for preliminary modifications such as, for example,transesterifications, of the triglycerides contained in them. Theprocess according to the invention, furthermore, is performed withoutthe need to add large quantities of water, which makes it even moreadvantageous from the industrial point of view.

The present invention relates to a process for the production ofmonocarboxylic saturated acids and triglycerides of saturated carboxylicacids having more than one acid function starting from non-modifiedvegetable oils containing triglycerides of unsaturated fatty acids,characterised by comprising the steps of:

-   -   (a) reacting the triglycerides of unsaturated fatty acids with        an oxidising compound in the presence of a catalyst for the        oxidation reaction of the olefinic double bond of the        unsaturated fatty acid, and obtaining a vicinal diol as an        intermediate product;    -   (b) reacting said intermediate product obtained from step (a)        with oxygen or a compound containing oxygen, in the presence of        a catalyst for the oxidation reaction of the two hydroxyl groups        of the vicinal diol to carboxylic groups, and obtaining a        reaction product comprising saturated monocarboxylic acids (i)        and triglycerides of saturated carboxylic acids having more than        one acid function (ii); said step (b) having a water/diol ratio        of below 1:1;    -   (c) separating said saturated monocarboxylic acids (i) from said        triglycerides of saturated carboxylic acids having more than one        acid function (ii).

According to another aspect of the invention, said step (b) has awater/diol ratio of below 1:3.

According to another aspect of the invention, during step (b) thereaction product is preferably present in form of an aqueous phase andan organic phase.

According to another aspect of the invention, said intermediate productobtained from step (a) is reacted with oxygen or a compound containingoxygen in step (b) without the need for any purification treatment.

According to a further aspect of the invention, said step (b) is carriedout without addition of water besides the water in which the catalyst isdissolved.

According to a still further aspect of the invention, both steps (a) and(b) are carried out without the addition of organic solvent.

The starting material for the process according to the present inventionis a vegetable oil comprising a mixture of triglycerides of unsaturatedfatty acids. Examples of vegetable oils are: soybean oil, olive oil,castor oil, sunflower oil, peanut oil, safflower oil, maize oil, palmoil, jatropha oil, cuphea oil, oils from Brassicaceae such as Crambeabyssinica, Brassica carinata, Brassica napus (colza), Lesquerella, oilswith high monounsaturated acid content etc. The use of sunflower oil andof oils from Brassicaceae is particularly advantageous. The use ofsunflower oil with high oleic acid content and of oils from Brassicaceaewith high erucic acid content is even more advantageous.

The fatty acid of the triglyceride can be monounsaturated orpolyunsaturated. Examples of unsaturated fatty acids are 9-tetradeconoic(myristoleic), 9-hexadecenoic (palmitoleic), 9-octadecenoic (oleic),12-hydroxy-9-octadecenoic (ricinoleic), 9-cicosenoic (gadoleic),13-docosenoic (erucic), 15-tetracoscenoic (nervonic),9,12-octadecadienoic (linoleic), and 9,12,15-octadecatrienoic(linolenic) acid.

Monounsaturated fatty acids are particularly preferred. In the processaccording to the invention use of oleic acid and of erucic acid isparticularly advantageous. In such a case pelargonic acid as saturatedmonocarboxylic acid is obtained as end product with high yields.

The oxidising compound used to perform step (a) of the process accordingto the invention is preferably an aqueous solution of hydrogen peroxidein concentrations of between 30 and 70 wt %, preferably between 35 and60 wt % and even more preferably between 40 and 50 wt %.

The diol resulting from step (a) is made to react—in step (b)—withoxygen or with a compound containing oxygen. The use of air isparticularly advantageous and the use of oxygen enriched air is evenmore advantageous.

Advantageously the catalyst of step (a) belongs to the group consistingof tungsten, molybdenum, and their acids and alkaline salts. The use oftungstic acid or phosphotungstic acid is particularly preferred. Saidcatalyst is present in quantities of between 0.03% and 3% by moles,preferably between 0.05% and 1.8% by moles and even more preferablybetween 0.06% and 1.5% by moles with respect to the unsaturated fattyacid.

As regards the catalyst of step (b), it can be added to the reactionmixture as aqueous solution and it belongs advantageously to the classof cobalt and/or manganese based compounds and their mixtures, such as,for example, acetates, chlorides, sulphates, bromides and nitrates, usedin quantities of between 0.05% and 3% by moles, preferably between 0.1%and 2% by moles and even more preferably between 0.3% and 1.5% by moleswith respect to the diol produced in step (a). The use of cobalt acetateand cobalt chloride is particularly preferred.

Advantageously as inorganic acid can be added to the cobalt-based orcobalt and manganese-based catalyst of step (b). Examples of inorganicacid are phosphoric acid, hydrochloric acid and perchloric acid andtheir mixtures.

As catalyst of step (b), manganese-based compounds can be advantageouslyused in a mixture with the cobalt-based compounds. Preferably, saidmixtures have a Co:Mn molar ratio comprised between 5:1 and 10:1.

In a preferred form of the process according to the invention, at thebeginning of step (a) a small addition of the intermediate that forms atthe end of step (a) (so-called reaction activator) is used, as theinitial presence of the intermediate that will form promotes activationof the reaction.

The “reaction activator” is added in a quantity ≦5%, preferably ≦3% byweight with respect to the starting oil.

Advantageously, if the reaction activator is not available, it is usefulto add to the initial reaction mixture a certain quantity of H₂O₂ andwait for the temperature to increase due to the exothermia of theprocess. When this happens it means that the reaction of the unsaturatedfatty acid part of the triglyceride with H₂O₂ has occurred and thereforethe dihydroxide that activates the reaction has formed.

In a preferred form of the process according to the invention, duringstep (a) nitrogen is fluxed to distil a part of the water of theprocess. This prevents excessive dilution of H₂O₂. An alternative tonitrogen flow is evaporation under reduced pressure.

In a preferred form of the process according to the invention at the endof step (a) the catalyst is not removed.

The reaction temperature of step (a) and step (b) of the present processis advantageously between 45 and 95° C., preferably between 50 and 90°C.

The reaction temperature of step (a) is advantageously between 55 and70° C.

The reaction temperature of step (b) is advantageously between 55 and90° C., more advantageously between 60 and 70° C.

The time necessary for the reaction of step (a) of the present processis between 2 and 10 hours while the time necessary for step (b) isbetween 3 and 12 hours.

The process according to the invention can be advantageously performedat atmospheric pressure or at low partial oxygen pressures, thereforeresulting particularly advantageous in terms of industrial production.

Step (a) is preferably performed at atmospheric pressure.

Step (b) is performed at a pressure greater than atmospheric pressureand preferably ≦20 atm, more preferably ≦15 atm.

When aqueous phase is present, its separation from the organic phase canbe performed either at the end of step (a) or at the end of step (b).Advantageously such separation is performed at the end of step (b). Theaqueous phase contains the catalyst of step (b), if necessary in amixture with the catalyst of step (a), which can then be recovered andoptionally recycled as catalyst of step (b).

The organic phase is a clear oil consisting of a mixture substantiallycomprising saturated monocarboxylic acids and triglycerides containingsaturated carboxylic acids having more than one acid function, saturatedmonocarboxylic acids present is the starting mixture and vicinal diolwhich forms at the end of step (a).

Advantageously the triglycerides can be separated from the saturatedmonocarboxylic acids by means of distillation processes of the latter.Steam distillation is particularly preferred.

The above mentioned triglycerides containing saturated carboxylic acidshaving more than one acid function, as such or in chemically modifiedforms, can be used as intermediates in the production of polymers,surface-active agents, lubricants, lubricant coformulants and drugcarriers. Triglycerides containing saturated carboxylic acids havingbetween 1.5 and 2.5 moles of acid groups per mole of triglyceride arepreferred.

Said triglycerides containing saturated carboxylic acids can bechemically modified, for example, by means of a reduction reaction wherethe carboxylic units of the triglyceride containing is converted tohydroxy groups or amine groups. Intermediates containing hydroxyl, aminoand other functional groups in the range 1.5-2.5 mole per mole oftriglyceride are preferred. Such chemically modified intermediates areobtainable with well known chemical reactions.

Such chemically modified intermediates as well as said triglyceridescontaining saturated carboxylic acids can be used as monomers for theproduction of polymers such as: polyesters, polyamides, polyesteramides, polyurethanes, polyester-urethanes.

Highly preferred are tryglicerides which contain between 1 and 2.5 molesof azelaic acid, sebacic acid, brassilic acid and their mixtures.

Triglycerides containing the saturated carboxylic acids having more thanone acid function can in turn be hydrolysed into glycerol and saturatedcarboxylic acids. The hydrolysis reaction can be performed throughdifferent methods such as hydrolysis with water, hydrolysis with strongacid ion exchange resins and enzyme catalyzed hydrolysis.

The hydrolysis with water, (ratio water/oil comprised between 1:1 and1:5) is performed at a temperature comprised between 150 and 300° C.,preferably between 180 and 270° C., at a pressure equal to theequilibrium pressure of the steam with or without adding hydrolysiscatalysts. The hydrolysis is performed at a temperature of 100-120° C.with strong acid ion exchange resins. Examples of such resins areAmberlyst® and Amberlite® type resins (both manufactured by Rohm andHaas Co.).

The enzyme catalyzed hydrolysis is performed with lipases. Said lipasescan be advantageously selected from the group comprising: Candidacylindracea, Candida antartica, Pseudomonas sp., porcine pancreaticlipase, Candida rugosa, Geotrichum candidum, Aspergillus niger, Mucormietei, Rhizopus arrhizus, Rhizopus delemar, Rhizopus niveus,Chromobacterium viscosum, Thermomyces lanugiaosus, Penicillum cyclopium.

Depending on the type of starting oil, different carboxylic acids can beobtained such as: oxalic acid, malonic acid, succinic acid, glutaricacid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacicacid, undecandicarboxylic acid, dodecandicarboxylic acid, brassylicacid, tetradecandicarboxylic acid, pentadecandicarboxylic acid.

In a preferred form of the process according to the invention, azelaicacid and brassylic acid are mainly obtained from the hydrolysisreaction, with yields of up to 80% with respect to the quantity ofsaturated carboxylic acids having more than one acid functiontheoretically obtainable.

The process according to the invention will now be described withreference to non-limiting examples below.

EXAMPLES Example 1

Step (a) (Reaction with H₂O₂)

The following substances were placed in a reactor:

-   -   1000 g of sunflower oil with high oleic content (82% oleic acid,        10% linoleic acid, 4.5% palmitic acid, 3.5% stearic acid),    -   5 g tungstic acid (0.7% by moles with respect to the unsaturated        fatty acid)    -   50 g of raw hydroxylated oil (intermediate obtained at the end        of step (a) coming from a previous reaction, so-called “reaction        activator”).

The temperature was increased to 60°-65° C. and 280 cc of 49.9% solutionof H₂O₂ were added in 3 h.

During the reaction nitrogen was fluxed to distil a part of the water ofthe process and to prevent excessive dilution of H₂O₂.

Once the addition of H₂O₂ was completed, the reaction was continued at65° C. for 3 h.

Step (b) (Reaction with Air)

The mixture formed at the end of step (a) was transferred to anautoclave provided with stirring system.

300 g of aqueous solution of 1% cobalt acetate were added (0.4% % bymoles with respect to the diol produced in step (a)). The temperaturewas increased to 70° C. and the reactor was brought to a pressure of 12atm with air. The air was continuously fluxed to provide a sufficientsupply of oxygen. The beginning of the reaction was highlighted by theincrease in temperature of the mixture due to the exothermia of theoxidative cleavage. The reaction lasted 8 h.

At the end of step (b) hot separation of the aqueous phase from theorganic phase was performed. The aqueous phase contained the catalystsof the first two reaction steps (tungstic acid and cobalt salts), whichcould be subsequently recovered.

The organic phase (oxidised oil) consisted of triglycerides containingmainly azelaic acid (together with smaller quantities of palmitic acid,stearic acid and dihydroxystearic acid) in a mixture with pelargonicacid and short-chain free monocarboxylic acids.

Step (c)

The organic phase was distilled by steam distillation to separate thelight fraction, consisting of 360 g of pelargonic acid and short-chainfree monocarboxylic acids.

The distillation residue (790 g) consisted mainly of triglycerides ofazelaic acid.

Example 2

The triglycerides remaining in the boiler at the end of the distillationas per example 1 step (c) were subjected to a hydrolysis reaction byadding water in a ratio 1:1 at 180° C. under pressure for 3 h. Thisreaction released the mono- and dicarboxylic saturated fatty acids fromglycerol. Azelaic acid and glycerol were separated from the mixture offatty acids by means of successive extractions with water at 90° C. Bycooling of the aqueous solution, 370 g of azelaic acid werecrystallised. The remaining water was passed through a basic ionicexchange resin and then evaporated to recover 100 g of glycerol.

The quantity of azelaic acid obtained, cross-checked by a gaschromatographic analysis, corresponded to a cleavage yield of the oleicacid equal to approximately 70% with respect to the quantity of azelaicacid theoretically obtainable.

1. Triglycerides containing saturated carboxylic acids having more thanone acid function, wherein said saturated carboxylic acids compriseazelaic acid and one or more of glutaric acid, adipic acid, pimelicacid, suberic acid, sebacic acid, undecandicarboxylic acid,dodecandicarboxylic acid, brassylic acid, tetradecandicarboxylic acid,pentadecandicarboxylic acid.
 2. Triglycerides according to claim 1having between 1 and 2.5 moles of acids groups per mole of triglyceride.3. Triglycerides according to claim 1, wherein the saturated carboxylicacids having more than one acid function are mixtures of azelaic acid,sebacic acid or brassylic acid.
 4. Triglycerides according to claim 1,wherein the carboxylic units are chemically modified to hydroxyl oramino group.
 5. A method for producing a polymer which comprisespolymerizing a triglyceride of saturated carboxylic acids according toclaim
 1. 6. A lubricating method which comprises applying to the surfaceto be lubricated a triglyceride of saturated carboxylic acids accordingto claim
 1. 7. A method for producing a surface active agent whichcomprises using a triglyceride of saturated carboxylic acids accordingto claim
 1. 8. A drug carrier composition which comprises a triglycerideof saturated carboxylic acids according to claim
 1. 9. A method forproducing a polymer selected from the group consisting of polyesters,polyamides, polyester-amides, polyurethanes, polyester-urethanes whichcomprises polymerizing a triglyceride of saturated carboxylic acidsaccording to claim
 1. 10. Chemically modified carboxylic acids obtainedfrom the hydrolysis reaction of triglycerides containing saturatedcarboxylic acids according to claim
 4. 11. A method for producing apolymer selected from the group consisting of polyesters, polyamides,polyester-amides, polyurethanes, polyester-urethanes which comprisespolymerizing a chemically modified carboxylic acid according to claim10.
 12. Triglycerides according to claim 2, wherein the carboxylic unitsare chemically modified to hydroxyl or amino group.
 13. Triglyceridesaccording to claim 3, wherein the carboxylic units are chemicallymodified to hydroxyl or amino group.
 14. A method for producing apolymer which comprises polymerizing a triglyceride of saturatedcarboxylic acids according to claim
 2. 15. A method for producing apolymer which comprises polymerizing a triglyceride of saturatedcarboxylic acids according to claim
 3. 16. A method for producing apolymer which comprises polymerizing a triglyceride of saturatedcarboxylic acids according to claim
 4. 17. A lubricating method whichcomprises applying to the surface to be lubricated a triglyceride ofsaturated carboxylic acids according to claim
 2. 18. A method forproducing a surface active agent which comprises using a triglyceride ofsaturated carboxylic acids according to claim
 2. 19. A drug carriercomposition which comprises a triglyceride of saturated carboxylic acidsaccording to claim
 1. 20. A method for producing a polymer selected fromthe group consisting of polyesters, polyamides, polyester-amides,polyurethanes, polyester-urethanes which comprises polymerizing atriglyceride of saturated carboxylic acids according to claim 1.